I have an old form that was not made by myself being fed with a CSV file, my client needs to add another merged field, I presume I could add this onto the end on one of the other fields as below:

Field 1#Field 2 (new)

I could then get PP design to merged to the left of the # for the old field and to the right for the new one although I'm unsure how to do this.

In excel it would be:
=RIGHT(A1,LEN(A1)-FIND("#",A1))
=LEFT(A1,FIND("#",A1)-1)

Many thanks